10. Acids and Bases
The pH Scale
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Hey guys. In this new video, we're going to put to practice some of the concepts we learned about pH and pOH. So let's take a look at the first example. Here it says, what is the hydroxide ion? So what's the Oh- and the hydrogen ion concentration or hydronium ion concentration actually? That's H+ of an aqueous solution that has a pH equal to 6.12. So, we have pH, we need to find Oh- and H plus Remember, we're able to derive a formula that connects us between H+PH. Remember that H+10- pH. All we have to do now is just take that number and plug it in. When we do that, we get 7.59x10 -seven. Now we could find Oh now and we can find Oh in 2 different ways. Now, the first way we could find Oh minus is by simply using this equation, kw equals H+ Oh-. We know what kw is. We assume the temperature is 25 degrees Celsius since they don't tell us what it is. This will be 1.0x10-fourteen. We just found out what H+ is. It's 7.59x10-seven. Now we have to find Oh- Oh- is our only missing variable, so just isolate it. So here, Oh- would equal 1.32x10-eight. So that'd be one way we can find Oh minus. Now, the second way we could find it is if we know pOH, we can make a connection between pOH and Oh minus. So first we'd say that pH +OH equals 14. We know pH is 6.12, so let's just isolate our pOH. Subtract 6.12 from both sides. So pOH equals 7.88. And remember, what's the connection between pOH and Oh-? You can just simply say that, Oh- equals 10 to the negative pOH. And if you did 10 to the negative 7.88, you get the same exact answer for Oh-. So 2 different methods to find the same exact missing variable. So it's basically your choice on deciding which way you want to go. Personally, I like to just find pOH and just do 10 to the negative pOH. Because remember, if you don't put these 2 in brackets, your calculator may give you the incorrect answer. So it's probably always safer just to say Oh- equals 10 to the negative pOH.
